The present invention relates to electronic keyboard musical instruments of the multiplexed variety, and in particular to a circult for generating a single data pulse synchronized with the multiplexed data stream, wherein the generated pulse bears a predetermined relationship to the keydown pulses in the multiplexed data stream.
In most electronic organs in use today, both the solo and accompaniment manuals are adapted for polyphonic operation wherein tones corresponding to all depressed keys of the keyboard are simultaneously sounded. In multiplexed organs, this is accomplished by cyclically scanning the accompaniment and/or solo manuals and generating one or more time division multiplexed serial data streams comprising time slots corresponding on a one-to-one basis to the keys of the keyboard and wherein keydown pulses appear in time slots corresponding to depressed keys of the keyboards. Thus, if three keys on the solo keyboard are depressed, the serial data stream will comprise three keydown pulses in the time slots corresponding to these keys. The data stream is fed to the serial data input of the demultiplexer wherein the serial data is converted to parallel format, and the parallel data is utilized to actuate respective keyers for keying tones from the tone generation system to the output circuitry of the organ.
Although polyphonic operation is utilized in most cases, there are certain instances wherein monophonic operation is desirable. For example, when the tones selected by the solo manual are voiced in a manner to simulate brass instruments, such as trumpets and trombones, if the brass tones are played as chords, they often sound muddy and unclear. Accordingly, brass is normally played monophonically, with one key being depressed at a time. Since most music is written in polyphonic form for the solo manual, however, this would require the player to manually select a single note from each chord which is written for the solo manual. To accomplish this selection in an automatic fashion, prior art systems have been developed whereby either the keyboard or the data stream is prioritized such that the highest note, for example, of a played chord will be sounded and the other notes remaining silent even though the corresponding keys are depressed.
Another instance in which detection of the highest note played on the solo manual is desirable, is that of solo fill note generation. In systems of this type, such as that disclosed in U.S. Pat. No. 3,990,339, the first occurring pulse in the solo data stream, which is generated by scanning the solo manual from the highest note to the lowest note, is detected. This note is played together with certain notes of the chord played on the accompaniment manual but sounded in the octave immediately below the highest note played on the solo manual.
In prior art systems for either converting from polyphonic to monophonic operation on the solo manual or for selecting the highest note played for use in a fill note generation system, the first occurring pulse in the multiplexed data stream is merely selected or detected rather than a corresponding high note data pulse generated. One of the problems with this occurs in multiplexing systems wherein the keydown pulses have a pulse width which is equal to the entire width of the time slot. Thus, if two adjacent keys are played, the two keydown pulses will appear as a single, wide pulse rather than two individual pulses because the trailing edge of the first occurring pulse and the leading edge of the second pulse are substantially coincident. In the priority system of U.S. Pat. No. 4,055,103, for example, only the first occurring pulse is passed, but the system is dependent on the occurrence of the trailing edge of the pulse to lockout the remaining pulses in the data stream. If this system were utilized to generate or detect a pulse which spans more than one time slot, the entire pulse would be permitted to pass, rather than just a single pulse occupying only the time slot coincident with the leading edge of the pulse.